Ballast arrangement for tank ships



y 3,1968 5. .1. GROCOTT I 3,385,251

BALLAST ARRANGEMENT FOR TANK SHIPS Filed June 23, 1967 2 Sheets-Sheet 1 FIG 7 5 o 74- 73 7, 1 f/ 76 Z f 12 4 A I I I II II I I I I A ,6/, W

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INVENTOR GEOFFREY JOSEPH GROCOTT MORGAN, FINNEGAN. DURHAM 8 PINE ATTORNEYS May 28, 1968 G. .1. GROCOTT 3,385,251

BALLAST ARRANGEMENT FOR TANK SHIPS Filed June 25, 1967 2 Sheets-Sheet 2 FIG. 3.

$5 I g! "I 3- INVENTOR GEOFFREY JOSEPH GROCOTT MORGAN FINNEGAN. DURHAM 8 PINE ATTORNEYS,

United States Patent 0 3,385,251 BALLAST ARRANGEMENT FUR TANK SHIPS Geoffrey Joseph Grocott, Bearstcd, Maidstone, Kent, England, assignor to The British Petroleum Company Limited, London, England, a corporation of England Fiied June 23, 1967, Ser. No. 648,309 Claims priority, application Great Britain, July 6, 1%6, 30,267/66 9 Claims. ((11. l14l25) ABSTRACT 0F THE DIStILOSURE A tank ship Contains a grating which supports a ballast bag in at least one of its cargo tanks. The grating supports the bag clear of the sump and the inlets and outlets in order to allow free access of cargo.

The arrangement is particularly useful for refrigerated tank ships since it eliminates the formation of ice and hydrocarbon hydrates in the cargo space.

This invention relates to a ballast arrangement for tank ships and more particularly to the prevention of contamination of the cargo tanks by ballast water placed therein and also the contamination of the ballast Water by any residue in the tank.

During an empty passage it is common practice to ballast an oil tank ship by means of sea water placed in the cargo tanks. The water is usually contaminated by the residue in the tank and this creates the problem of purifying the ballast water before it is dumped. It is wellknown that inadequate purification causes contamination of the sea and hence of beaches.

In the case of refrigerated gas tank ships, e.g. butane carriers, the contamination of the tanks is more important than the contamination of the water. When cold cargo is placed in the tank the water freezes and this may cause various difficulties, e.g. blockage of cargo inlets and outlets by ice and also the cracking of water pipes and water pumps due to expansion. It is therefore common for refrigerated tank ships to be provided with separate ballast tanks and these may amount to 20% of the total capacity of the vessel. During loaded voyages it may be necessary to use half the capacity of these tanks to provide trim but it appears that a 10% increase in the capacity of a refrigerated tank ship could be achieved by a solution of the contamination problem.

it is an object of this invention to reduce both of the contamination difliculties mentioned above.

According to the invention at least one of the cargo tanks of a tank Ship contains secured therein a collapsible ballast bag suitable for containing ballast water, each bag being supported upon a grating situated near the bottom of the tank whereby the ballast bag is supported clear of the sump and the inlets and outlets so as to allow free acccess of cargo.

The ballast system according to the invention may be used to provide the entire ballast requirement of the vessel or the system may be used to provide only a part of the requirement, thus in a tank ship a portion e.g. half, the ballast requirement may be provided according to the invention and the remainder by ballast tanks which can be used during loaded voyages for trim.

All the cargo tanks of a tank ship may be provided with a ballast arrangement according to the invention but this is not necessary provided the total capacity is sufficient. It is preferred that every cargo tank which is provided with a ballast system in accordance with the invention is pro vided with a single ballast bag.

In the case of refrigerated tank ships it is preferred to provide ballast pumps situated inside the cargo tanks near to the ballast bags, the pumps being connected to the bag and to the deck of the vessel to provide for the transference of ballast water.

Ballast bags which are suitable for use according to the invention are commercially available. These bags consist of two rectangular sheets of flexible water-proof material which are joined together round the edges to form a water-tight seam, an inlet being provided in the centre of one of the sheets. The sheets may consist of fabric which is impregnated with rubber or plastic. It is, of course, important to choose the flexible sheets which retain their flexibility at the temperature of operation.

The invention also includes tank ships one or more of whose cargo tanks contain a grating positioned near the bottom which is adapted to support a ballast bag as described above.

A refrigerated tank ship fitted with a ballast arrangement according to the invention will now be described by way of example with reference to the drawings in which:

FIGURE 1 is a transverse section through a cargo tank fitted according to the invention,

FIGURE 2 is a longitudinal section of the tank shown in FIGURE 1,

FIGURES 3 and 4 show greater details of the grating which appears in FIGURES l and 2, and

FIGURE 5 is a perspective drawing of the bag and its harness which appears in FIGURES l and 2.

The cargo tank illustrated in FIGURES 1 and 2 contains a collapsible ballast bag 1t) which is supported on a grating 11 whose structure will be more fully described with reference to FIGURES 3 and 4.

The particular installation described is designed for carrying liquid butane and therefore the cargo tank is provided with thermal insulation 12 in order to reduce heat transfer. The heat transfer tends to occur to the greatest extent through the sides and base of the tank because these are in contact with the cold liquid cargo and also with the sea outside the vessel. For this reason it is conventional to avoid apertures in the walls and floor of the tank and therefore the ballast pipe 13 and the cargo pipe 14 pass through a hatch 15 situated in the roof. Since the depth of the tank is greater than the barometric height the tank also contains the ballast pump 16 and the cargo pump 17 and these are supported by their respective pipes 13 and 14.

The cargo pump 17 is situated near the bottom of the tank in the sump 18 and it is provided with an inlet 19 (which also serves as an outlet). As can be seen from FIGURE 2 the grating 11 curves upward over the sump so as to ensure that the ballast bag 10 in its collapsed position cannot block the inlet 19.

The ballast pump 16 is connected to the ballast bag 10 by means of a non-collapsible, flexible hose 20. At deck level the ballast pipe 13 branches to provide an air inlet 21 and a water-inlet 22 (both of which also serve as outlets).

At the start of an empty voyage the ballast bag 10 is filled with water obtained via the water inlet 22 (the ballast pump 16 is a centrifugal pump which allows passage of the water), and after filling the bag is in the condition shown in the drawings. At the end of the empty voyage the pump is primed and the water pumped out through the inlet 22. When the pumping ceases the air inlet 21 is opened and this allows the water in the pipes 13 and 21) as well as the pump 16 to drain into the ballast bag It). This is important because any water contained in the tank will freeze when the cargo of liquid butane is introduced. It is of no importance if the ballast bag contains some water because the bag is flexible and can therefore accommodate the expansion but the pipes 13 and and the pump 16 could be damaged if they were full of water at the time of freezing. It should be noted that it does not matter if they are wet provided that there is plenty of room for expansion.

The grating 11 must be of sufiicient size and strength to bear the weight of the bag when full and it must also be sufiiciently permeable to allow the drainage of cargo into the sump. The grating should have a smooth contoured top surface to minimise the risk of damage ot the ballast bag and it is preferred that the area which actually supports the bag be fiat. The grating should be curved to prevent access of the bag to any undesired portions of the cargo tanks; thus in FIGURES 1 and 2 the grating is curved over the sump to allow plenty of clearance.

As shown in FIGURES 3 and 4 the grating is conveniently constructed out of T-girders 23 which are laid parallel to one another and which are supported on crossbeams 24. Suitable dimensions to allow proper drainage of cargo are 6 inches for the heads of the Ts with about 2-inch gaps. The grating is situated about 6-12 inches from the bottom of the tank and the T-girders 23 and the beams 24 are curved upwards to provide extra clearance at the sump 18.

As can be seen from FIGURE 5 the bag is formed of two rectangular sheets of fabric (which may be laminated out of several layers) which have been impregnated with a synthetic rubber to prevent the escape of water. The two sheets are joined together at their edges by an overlap seam 27 which was bonded prior to vulcanisation. This produces a bag which collapses to a flat rectangular sheet when it is empty. The upper sheet is provided with a hose attachment 28 which enables water to be admitted into the bag which opens out to the configuration shown in FIGURE 4. (Bags of this nature are available commercially.) This arrangement gives very little chance of trapping cargo when the vessel is unloaded after a voyage.

The bag is held inside a harness which comprises two longitudinal encircling straps 29 and 30 and several encircling cross-straps 31. These straps are secured to one another at every crossing and tie-straps 32 are attached at the crossings on top of the bag. The tie-straps are used to fasten tie lines when the bag is secured inside a cargo tank.

I claim:

1. A tankship at least one of whose cargo tanks contains secured therein at least one collapsible ballast bag suitable for containing ballast water, each bag being supported upon a grating positioned near the bottom of the tank whereby the ballast bag is supported clear of the sump and the inlets and outlets so as to allow free access of cargo.

2. A tank ship according to claim 1, in which every cargo tank which contains a ballast bag contains a single ballast bag supported upon a single grating.

3. A tank ship according to claim 2, in which every cargo tank is provided with single ballast bag supported upon a single grating.

4. A tank ship according to claim 1, in which the tank ship comprises separate ballast tanks which are reserved for ballast water.

5. A refrigerated tank ship whose cargo tanks are provided with refrigeration means so that it can carry liquified petroleum gases at a temperature below the freezing point of water at least one of said cargo tanks containing secured therein at least one collapsible ballast bag suitable for containing ballast water, each bag being supported upon a grating positioned near the bottom of the tank whereby the ballast bag is supported clear of the sump and the inlets and outlets so as to allow free access of cargo.

6. The tank ship according to claim 5, in which every cargo tank which contains a ballast bag contains a single ballast bag supported upon a single grating.

7. A tank ship according to claim 6, in which every cargo tank is provided with a single ballast bag supported upon a single grating.

8. A tank ship according to claim 5, in which the tank ship comprises separate ballast tanks which are reserved for ballast water.

9. A refrigerated tank ship according to claim 5, which comprises water pumps for emptying the ballast bags and said pumps are situated inside the cargo tanks so as to reduce the head of water between the pump and the ballast bag.

References Cited MILTON BUCHLER, Primary Examiner.

T. M. BLIX, Assistant Examiner. 

